Smart insects stay a step ahead
of insecticidesHarender RajTHE
annual crop loss due to pests in India was estimated at Rs 60,000
million in 1983, which at today’s prices could exceed Rs 2,00,000
million. The loss due to just one species, Helicoverpa armigera (Heliothis
armigera), which attacks a number of important crops like cotton,
tomato, brinjal, chick-pea, cabbage, cauliflower, okra and even fruits
like strawberry and apple, is estimated to be over Rs 10,000 million per
year.

Knowing labels can save livesDivender Gupta
EVERY pesticide container
carries certain information on its label. This information includes the
trade name, technical name, composition, manufacturer’s address,
registered uses, date of packing, date of expiry, and toxicity label,
and is mandatory under the Insecticide Act, 1968.

‘Double grain output in 10 years’A
renowned agriculture scientist has warned India’s food security will
become unsustainable unless output is doubled to over 400 million tonnes
in 10 years.

ECO FARMINGBacteria may fight nematodesR.S. Kanwar and R.K. WaliaPLANT
parasitic nematodes are microscopic organisms, ubiquitous in nature,
which cause severe damage to our crops. There is hardly any plant that
is not attacked by them. Under heavy nematode infestation, there may be
total crop failure. Crop rotation, clean cultivation, fallowing and
summer ploughing are the traditional methods of nematode control.

THE
annual crop loss due to pests in India was estimated at Rs 60,000
million in 1983, which at today’s prices could exceed Rs 2,00,000
million. The loss due to just one species, Helicoverpa armigera (Heliothis
armigera), which attacks a number of important crops like cotton,
tomato, brinjal, chick-pea, cabbage, cauliflower, okra and even fruits
like strawberry and apple, is estimated to be over Rs 10,000 million
per year. The question is whether pesticides can be the answer to this
menace. The answer cannot be in the affirmative. As pesticide
consumption in India increased from 434 metric tones in 1954 to over
90,000 metric tones till 2001, resistance to pesticides is now known
in over 504 insect and mite pests in comparison to only seven
insect-pests in 1954.

Insects’ defence

Among all insect pests,
Helicoverpa is the most serious pest and is not affected much by
pesticides. It wreaks havoc by turning into its victims’ defences.

Now researchers at the
University of Illinois, USA, have discovered the secret of the earworm’s
(Helicoverpa zea) success. When the pest starts munching on a plant,
it immediately activates the plant’s natural defences. First,
signalling chemicals called jasmonate and salicylate are released
inside the plant. These chemicals then stimulate the production of
toxins within the plant that should kill the pest when it eats them.
However, researchers have found, the earworm can stay one step ahead
of the plant’s defences. Jasmonate and salicylate, that are vital to
triggering the plant’s defence, also switch on a set of genes inside
the pest. These genes lead to the production of enzymes in this insect’s
gut that break down the plant’s toxins as well as many synthetic
pesticides into harmless by-products. The enzymes render the plant’s
toxins useless before the plant has even had time to make them.

This recent discovery of
the earworm’s trick is the first evidence that insects can eavesdrop
on plant’s defences. It could be bad news for commercial pesticide
manufacturers who are keen to develop next-generation insecticides
that work by mimicking salicylate and jasmonate.

Widespread use of DDT (dichloro
diphenyl trichloro ethane) to control mosquitoes, fruit flies and crop
pests has also forced these insects to adapt to the wrath of the
pesticide. A single genetic mutation protects fruit flies from the
lethal effects of DDT and this genetic trait has spread around the
world among fruit flies like wildfire. Surprisingly, every resistant
fly had precisely the same genetic change, the addition of a
"jumping gene", a short sequence of DNA (dioxy-ribose
nucleic acid) that can insert itself into new locations in the genome.

The researchers found
this extra bit of DNA very near a gene coding for an enzyme that
munches up harmful chemicals. The mutation somehow prompts this gene
to create 100 times more of this enzyme than normal. The researchers
could not find mutation in any fly strains collected in the 1930’s,
prior to the use of DDT.

It is very surprising
that a single gene is responsible for all DDT resistance and the
mutation has stuck around even in laboratory strains that never
encountered DDT. This means that it could be very difficult to
eliminate resistance to an insecticide even if you stopped using it.
The discovery echoes similar research on the mosquito (Anopheles
gambiae) that carries the malaria parasite. Scientists recently found
that a DDT-resistance gene in mosquito had spread right up and down
the West Coast of tropical Africa.

Such rapid spread
suggests that resistance to new insecticides is inevitable and
impossible to stop, particularly for insects that travel around the
world with people or food.

Judicious use

Injudicious use of
pesticides has resulted in a number of serious detrimental side
effects. There are more and more reports of resistance to pesticides.
The number of pest and disease outbreaks has increased (resurgence)
and many innocuous insect species and pathogens have attained the
status of serious pests/diseases in recent years. The contamination of
soil, water and air is increasing to alarming proportions.

Another point of concern
is the detection of pesticide residues in almost all types of food
materials. In 1962, Rachel Carson in her book Silent Spring aroused
worldwide concern about the excessive use of pesticides which
eventually led to the concept of integrated pest management as an
environmentally sound alternative to the sole use of chemicals.

Agenda 21 of the United
Nations Conference on Environment and Development at Rio de Janeiro in
June 1992 identified integrated pest management and control in
agriculture as one of the requirements for promoting sustainable
agriculture and rural development.

An integrated strategy
for crop pest and disease management includes modifying organic
practices to evade and reduce pest/diseases incidence, biological
control, soil solarisation and other novel approaches for pest and
disease suppression and only need-based and judicious use of chemical
pesticides.

EVERY
pesticide container carries certain information on its label. This
information includes the trade name, technical name, composition,
manufacturer’s address, registered uses, date of packing, date of
expiry, and toxicity label, and is mandatory under the Insecticide
Act, 1968.

A toxicity label on a
container conveys the toxicity hazard of the pesticide to mammals,
mainly human beings, which is shown in a square—set at an angle of
45`B0—or a diamond, divided into two equal inverse triangles. The
lower triangle is brightly coloured whereas the upper contains warning
words and signals. The warning words are always written outside the
upper triangle whereas the signal words can be given either inside or
outside the triangle.

There are four toxicity
classes of pesticides, which are represented by bright red, yellow,
blue and green colours in the lower triangle—their toxicity
decreases in that order. A look at the colour of the lower triangle
can give us an idea of its toxicity to humans.

The hazard ratings, or
the toxicity classes, are based on the acute toxicity represented by
LD50 (median lethal dose) values. The LD50 value
is nothing but "the dose of the pesticide (active ingredient)
required to kill 50 per cent or the test population, generally rats,
when orally treated," and is expressed as mg/kg of the body
weight.

Lesser the LD50
value more toxic the pesticide is and vice versa; e.g., a pesticide
with a LD50 value of 10 will be more toxic than the
pesticide having an LD50 value of 100—in other words, for
a person weighing 60 kg a dose of 600 mg of active ingredient of the
former category of pesticide will prove fatal, whereas in the latter
case a dose of 6000 mg is required for the same.

Except for Bt (Dipel,
Halt, etc.) and plant-based formulations (neem formulations), no
insecticide is provided with a green label, whereas many of the
fungicides, bactericides and herbicides carry the green label and most
of them are in the category of blue or green.

Most of the
pesticide-poisoning accidents result from carelessness or ignorance in
handling chemicals. One should take utmost care while dealing with the
red-labelled pesticides, followed by yellow and blue. Green-labelled
pesticides are relatively safe, but that does not mean that we need
not take any care while using them.

A
renowned agriculture scientist has warned India’s food security will
become unsustainable unless output is doubled to over 400 million
tonnes in 10 years.

This acceleration will
have to come despite diminishing land resources, increasing biotic and
abiotic stresses, natural shrinkage and degradation, climate change,
rising input cost, loss of bio-diversity and burgeoning population,
the scientist, R S Paroda, has said in his new publication.

Against a projected
requirement of 230 million tonne foodgrains, according to Paroda’s
book Sustaining Our Food Security, the actual output this year
is likely to be only 191 million tonnes.

Paroda, a former
Director-General of the Indian Council of Agricultural Research (ICAR),
has made the projection keeping in view the rate of population,
income, demand of food, fodder, seed, industrial and other uses.

In a compilation of his
lectures and papers, Paroda cautions that the targets will not be
achievable unless major support is given to rainfed areas,
particularly in East India and other unfavourable regions where
technological, socio-economic and infrastructure bottlenecks exist.

The 775-page tome has
forewords by renowned agri-experts Norman E. Borlaug and M.S.
Swaminathan and will be formally released by Agriculture Minister Ajit
Singh in a few days.

The book comprises seven
parts and takes up a number of issues, including achievements and
potential of rice production in Asia and sustainability and
productivity of the rice-wheat system.

The book tells us how
the profitability of the rice-wheat system, as of rice and wheat
separately, has been declining since the pattern was adopted in late
1960s and early 1970s.

This, it says, is due to
a long-term decline in ‘real’ rice and wheat prices, decelerating
yield growths and increasing input costs. The price fall in the past
20 years is mainly due to domestic production outpacing population
growth, thus eliminating or lessening imports.

However, in wheat, due
to low global prices and rapid industrialisation, several Asia-Pacific
countries find it more cost-effective to import rather than produce.

The problem of rice
availability in the Asia-Pacific region would appear to have been
solved, but there is no room for complacency, it warns.

Genetic resources

One of the seven parts
of the book deals with conserving genetic resources with three
write-ups, including one titled "Is Global Conflict on Plant
Genetic Resources Justified?"

Genetic resources
collection and conservation activities have intensified since the
establishment of the International Board for Plant Genetic Resources
in 1974.

The conflict is between
haves and have-nots, since most of the genetic resources come from the
developing world but were conserved mainly in the gene banks of the
developed nations, leading to heated debates and arguments world wide.

The Global Biodiversity
Convention stipulates exchange of genetic material to be regulated
among countries on mutually agreed terms. Hence, what is needed now is
to develop appropriate guidelines for this purpose rather than to have
a North-South divide on the subject.

There is also a conflict
of rights. While plant breeding in developing countries has remained
largely in the public sector, a major role is played by the private
sector in the industrialised countries.

For their survival and
growth, private companies have to protect their rights on varieties so
developed in the form of different systems of intellectual property
rights (IPR).

Paroda feels a sui
generis system of varietal protection should be generated that
ensures recognition and reward for the informal innovations in the
form of "farmers’ rights," including ones to keep and
plant their own seeds.

Being a compilation of
lectures already given and papers already presented, the work may seem
to be a ‘copy and paste’ job. Nevertheless, it has a wealth of
information on policy reforms, food security, natural resource
management and importance of national and international partnership in
agricultural research.

Biotechnology

At a time when India
needs to accelerate production from five to 10 million tonnes per
year, productivity is still quite low, the book points out.

"But how does one
increase it? By using more water, nutrients and pesticides, or by
considering other alternatives?"

It is in this direction
that there is a tremendous potential by way of new products and
processes offered by biotechnology, a tool to supplement one’s
efforts. While working on transgenic crops, traits of interest from
the Indian point of view are herbicide tolerance and insect
resistance.

The loss on account of
weeds is between 15 and 30 per cent. The problem by and large is
overcome by manual weeding, yet insect-pest damage in cotton crops is
high and the crop needs 50 per cent of the entire nation’s pesticide
application.

"By transferring Bt
genes into plants, we can virtually build an insecticide factory
inside the plant," it says.

How biotechnology is
used, for good or bad, lies in the hands of mankind. Even the ‘terminator’
gene could prove to be very effective in controlling weeds like
parthenium, a nuisance to cultivated crops, the book argues. PTI

There is hardly any
plant that is not attacked by them. Under heavy nematode infestation,
there may be total crop failure. Crop rotation, clean cultivation,
fallowing and summer ploughing are the traditional methods of nematode
control. Use of nematicides for nematode control is very rare due to
their prohibitive costs, environmental pollution, adverse effects on
non-target organisms and residue problems in food and feed.

Research on the use of
botanical and microbial pesticides is being encouraged. Some fungi and
bacteria have been found acting as parasites on nematodes. But none
could be exploited to control nematodes under field conditions. A few
years ago, a bacterial parasite (Pasteuria penetrans) of nematodes was
discovered. This nematode-parasitic bacterium is highly specific to
its host and its life cycle is synchronised with that nematode. The
bacterial spores are non-motile. When a nematode wandering in soil
comes in contact with these spores they get attached to its body
cuticle. Not all kinds of nematodes are attacked by a single type of
bacterium.

The bacterium-nematode
relationship has been well studied in root-knot, a polyphagous
nematode. When the nematode larvae enter the root and start feeding
the spore terminates and pierces the nematode cuticle, and the spore
material (DNA strands and cytoplasmic mass) is passed into the
nematode body fluid. The spore gives rise to a ball-shaped mycelial
colony which fragments into daughter colonies to fill the entire
nematode body fluid. The nematode grows normally to reach adulthood,
by which time the bacterium multiplies inside to produce millions of
spores again. The nematode reproductive system becomes defunct and is
rendered infertile. Consequently there is no egg production. The
spores from the nematode carcass are released in soil upon root decay
and again infect the nematodes wandering in soil.

Spores of the bacterium
are host specific and can survive in soil for several years,
withstanding even adverse conditions.

This bacterium can be
used as a potential bio-control agent of plant parasitic nematodes,
especially the root-knot nematodes. Preliminary studies have shown
encouraging results. Current methods of multiplying the bacterium
under in vivo conditions for small-scale application already exist.
Efforts are being made to culture it on synthetic media under
laboratory conditions. Once its mass multiplication technique is
developed, it would be very useful for large-scale management of
nematodes in field horticultural crops.